This invention relates to methods of relieving the earth pressure in a working area in an underground coal or other mins.
For example, in longwall coal mining, are excessively large earth pressure is often met in the vicinity of a working area particularly in cases where the working depth from surface is substantially increased and may possibly cause bulging collapse of the coal face, which seriously impairs the mining efficiency. In coping with such situations, it has been usual to take measures such as of increasing the pressure-bearing capacity of the support structure, adding protecting devices thereto, or restricting entrance of miners to the working area for mining safety.
Under the circumstances, the present invention is intended to make any measures conventionally taken for prevention of such face bulging collapse as described above substantially needless or at least to minimize the need for taking the conventional preventive measures.
According to the present invention, there is provided a new method of relieving the earth pressure around a working area, which is applicable to underground excavation of ore deposits under which a weak stratum lies and which comprises injecting high-pressure liquid into the underlying weak stratum to enlarge the stress envelope formed around the working area thereby to alleviate the earth pressure at the working face.
The above and other objects, features and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawing.